Hair straightener



FIG. 1 is a perspective view of a hair straightener showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left elevational view thereof;

FIG. 5 is a right elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The dashed or broken lines where present illustrate portions of the hair straightener that form no part of the claimed design. 

CLAIM The ornamental design for a hair straightener, as shown and described. 